In MLB and NFL it's better to have a deep team and be stocked up and down through the lineup because the weighted average of a player is much smaller in those sports. In the NBA it is much more important to have stars at your top few positions. In baseball the best pitcher pitches only once every 5 days. In football, you can mask your deficiencies through the schemes that you run and your style of play. In basketball you cannot do this. Your stars are out there in every game and in almost every important play.

It's one of the reasons why when people talk about all time matchups many people will say "I'll take Jordan + 4 scrubs over any other combination of players ever." That one star is that important in basketball.

Not entirely true, in football having a great QB can take you a long way, just look at Peyton.